The proposed study will investigate the relationship between respiratory impairment and (1) sleep abnormalities, (2) magnitude of change in oxygen saturation (SaO2) and end-expired carbon dioxide (PeCO2), and (3) breathing patterns during sleep. The relationships will be studied in 60 non-hospitalized male patients with varying sevezity of chronic obstructive pulmonary disease (COPD) and the results compared with those from 30 age-matched healthy men. Pulmonary function and arterial blood gas studies as well as ventilatory response to hypoxia and hypercarbia during waking will serve as predictor variables. Their relationship to the following sleep related variables will be examined: frequency of arousals, awakenings, and stage changes to lighter sleep, duration of sleep stages and distribution of sleep time among stages; respiratory variables, i.e. frequency and duration of apneas and hypofeas, mean and peak minute ventilation (V1) and respiratory rate; mean and peak levels of oxygen desaturation and end-expired CO2, and frequency and duration of peak changes in oxygen desaturation and end-expired CO2; arousal thresholds: levels of SaO2, end-expired CO2 and V1 associated with arousals and stage shifts. Interrelationship between the variables will be analyzed within subject groups characterized by severity of respiratory impairment and age. Variability in sleep and respiratory variables within and between two consecutive nights will be examined. The findings should facilitate identification of patients at risk for impaired sleep and respiratory function during sleep. They may also reveal the conditions when respiratory dysfunction can be expected and may suggest criteria for assessing need for oxygen therapy during sleep. Such information would be useful not only for patients with COPD, but also for those with acute cardiopulmonary conditions that impair respiratory function.